Patrones de articulaciones plásticas en pórticos de hormigón reforzado de mediana altura sujetos a terremotos

Este trabajo presenta un estudio de pórticos de hormigón armado sometidos a terremotos para determinar las regiones de estos pórticos que llegan al rango ineslástico. Se estudio la respuesta no-lineal de pórticos de diez niveles diseñados para distintas cargas laterales y sometidos a cinco terremotos diferentes. Se encontró que en los pórticos regulares que llegaron al rango inelástico se forman articulaciones plásticas hasta en los niveles altos de estructura debido a la influencia del segundo modo de vibración en la respuesta de los pórticos (AU)

Simulación numérica de la respuesta sísmica del sistema tridimensional acoplado edificio - rieles - contrapeso de un ascensor

Los ascensores son componentes no estructurales de edificios que muchas veces cumplen funciones de vital importancia como es el caso de aquellos localizadores en hospitales. Así como el edificio puede ser afectado por un movimiento sísmico fuerte, tambien los ascensores pueden sufrir daños. Durante el terremoto de 1971 en San Fernando, California, cientos de ascensores fueron severamente dañados en el área de Los Angeles. Esto hizo que por primera vez se incorporaran en los códigos para diseño e instalación de asensores medidas para tener en cuenta el efecto de los terremotos. Si bien los daños reportados durante terremotos subsiguientes en California disminuyeron, todavía se observaron numerosas fallas. La falla más común fue el descarrilamiento del contrapeso en los ascensores eléctricos, seguida por la deformación permanente de los rieles. Este proyecto de investigación pretende explicar el comportamiento de los contrapesos durante un terremoto fuerte mediante una simulación numérica. Se desarrollo un modelo de un edificio multipiso en donde se incluye un modelo de contrapeso y sus dos rieles. El edificio se sometio a la aceleración en la base registrada durante un terremoto histórico para obtener la respuesta en el tiempo. Los resultados confirman que, a no ser que se implementen medidas especiales, el sistema riel - contrapeso va a fallar debido al mismo. El modelo desarrollado y metodología usada para calcular la respuesta pueden ser útiles para estudiar cómo reforzar los ascensores para que resistan mejor los movimientos sísmicos ÿ(AU)

Evaluación de la vulnerabilidad del Puente Warth en Austria

El Puente Warth fue diseñado y construido a pricipios de los años setenta, con códigos sísmicos ahora obsoletos. Por lo tanto, era necesario una revisión de su comportamiento actual para la toma de futuras decisiones sobre su mantenimiento o rehabilitación. En este artículo se muestra el análisis realizado para definir la vulnerabilidad sísmica de esta estructura, considerando un método simplificado de evaluación del daño máximo y la aplicación de la simulación por Monte Carlo para definir la respuesta probable del puente. En este análisis, se tomaron en cuenta las incertidumbres inherentes a las propiedades estructurales y a la excitación sísmica externa, mediante dos escenarios sísmicos. Los resultados obtenidos muestran que bajo algunas condiciones de carga deberían ser consideradas posibles reparaciones moderadas(AU)

Development of measurement capability for micro-vibration evaluation with application to chip fabrication facilities

In this project, Multidisciplinary Center of Earthquake Engineering Research (MCEER) researchers conducted vibration tests at a site in West Seneca, New York to determine its suitability for attracting and supporting a ChipFab facility. ChiFab, a short name for a semiconducto chip fabrication facility, is high-tech manufactuing facility where the electronic chips for items ranging from computers to cellular phones to automobiles are manufactured. The industrial park site (North America Park) is located near a railroad, a major expressway and an active mining operation. The level of micro-vibrations of ground motion is critical for this type of facility. Several locations were instrumented within the industrial park. Three direction acceleration components were measured at each location, during the period between November 1 and December 1, 1998. These acceleration data were subsequently converted into RMS velocity (one-thrid-octave band) through specially derived analytical relationships. It was found that the proposed ChipFab site in the northen section of the industrial park was suitable for the manufactuting facility. The measurement system used to conduct this testing was developed specifically for this project. This report describes the measurement system detail, including its sensory system, data acquisition and recording, sensor installation and distribution of the measurement locations. The procedure to obtain measurements, data evaluation, and results and analyses related to the West Seneca site are also described in the report. In addition to the encouraging results at the specific site (North America Center, West Seneca, NY), the ground vibration measuring procedure developed can potentially be used as an industrial standard for delicate manufacturing site evaluation. The report also introduces the theorical development for the relationship between frequency spectra and RMS values, which can be adopted for a wide range of applications on interpretations of the data obtained from up-to-date data acquisition systems

Design and retrofit methodology for building structures witn supplemental energy dissipating systems

The study described in this report on focuses on fundamental issues related to the design and use of supplemental damping devices in building structures. The principle objective is to develop a generic/practical analysis and design methodoly for structures that considers structural velocities and equivalent viscous damping of the devices. These two issues are explored in depth. Tools to transform the spectral velocity to an actual relative structural velocity are provided, and simple design procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. The effectiveness of the design methodology is demonstrated with a retrofit design example using a supplemental load balancing tendom configuration

Critical seismic issues for existing steet bridges

This report assesses the perfomance of existing steel bridges in the past earthquakes. There is an identification of the areas in existing steel bridge structures that are seismically vulnerable. Among the examined components there are: steel columns, steel tower bents, steel superstructures (particularly steel trusses), girder cross-frames, and steel connections. Vulnerable areas and details are identified, and recommendations for improved designs and retrofit techniques are made. Research needs are identified where existing knowledge is lacking. There is an examination of the three most common lateral force existing systems: MRF's: moment resisting frames; CBF's: concentrically braced frames and EBF's; eccentrically braced frames. It indicates that any of them can provide adequate seismic structural ductility. There is also an analysis of X-braces and X-braces and V-braced bridges piers as a way of getting potential structural ductility. It has a lis of illustrations, which include configurations, pier designs, axial loads and analytical models of connections, among others

Minimum design loads for buildings and other structures

ASCE standard, Minimun Design Loads for Buildings and Other Structures (ASCE 7-98), gives requirements for dead, live, soil, flood, wind, snow, rain, ice, and earthquake loads, and their combinations, that are suitable for inclusion in building codes and other documents. ASCE 7-98 is a revision of ASCE 7-95. Substancial changes were made to the wind, snow, earthquake, and ice provisions. In addition, substancial new material was added regarding the determination of flood loads. The structural loading requirements provided by this standard are intended for use by architects, structural engineers, and those engaged in preparing and administering local building codes. (AU)